1. Preheat oven to 325F (160). Grease 7-inch (18cm) round cake pan with butter, line the bottom with parchment paper. Grease the parchment as well. Set aside.2. Chop the chocolate, place in a heatproof bowl. Set the bowl over a pot with simmering water (double boiler) and melt completely. Also you can melt in 20 second pulses in the microwave. Remove the bowl from heat and let cool slightly.3. In a separate bowl, beat the egg whites until soft peaks form.4. Add the egg yolks, one at the time to the chocolate and stir until combined.5. Fold 1/3 of the egg whites into the chocolate mixture, then, repeat two more times.6. Pour the batter into prepared pan.7. Bake for 28-30 minutes.8. Let cool, dust with powdered sugar and serve.Notes:
For extra airy cake add 1 more egg white.
If this cake is too bitter, you can add few tablespoons of white/brown sugar.